Williams says the firm knows from years of experience with open enrollment for Medicare patients, that the Monday after Thanksgiving is always the single busiest day for business.

"People will have been thinking about this over the holidays and talking to family members, and they are going to feel an impetus to do something on that Monday; and there is going to be a huge crush," he said.

Why December? Well, it finally represents a deadline. Originally you had to sign up by Dec. 15 in order to have your insurance coverage begin Jan. 1. Last week the administration extended the deadline to Dec. 23.

Robert Laszewski, who runs his own health consulting firm, Health Policy and Strategy Associates, says there are still two big groups that will try to squeeze through the tight enrollment window.

One group includes those who have received cancellation notices from their insurance companies and who need insurance that meets the health law's new requirements.

The other group includes people who have been shut out of coverage until now because of pre-existing conditions and who have been waiting for HealthCare.gov to get its act together.

"We've got all these people that have been sitting desperately next to their computers trying to get enrolled in guaranteed-issue health insurance that has subsidies for the first time in American history," said Laszewski. "And they're looking forward to coverage on Jan. 1."

The administration says it's ready — or will be by its self-imposed Nov. 30 deadline. The website should be able to handle 50,000 users at the same time by the end of this month, HealthCare.gov repair czar Jeffrey Zients told reporters in a conference call Friday. That would double its current capacity.

But he said the administration isn't depending on the website alone to handle the traffic surged expected in December. "We're also beefing up additional paths for enrollment — through the call centers, in-person assistance, and ... direct enrollment with issuers," he said.

When Zients talked about direct enrollment, he meant allowing individual insurance companies, as well as large Web-based brokers, to sign up people so they don't even have to visit the federal website. Right now that can happen for people who aren't eligible for government subsidies to help them afford coverage. But subsidy calculations still have to run through HealthCare.gov.

That frustrates people like Towers Watson's Williams. His company is one of five major Web brokers that was supposed to be helping enroll people, but it hasn't been able to sign up those eligible for subsidies because the technology to help their websites connect to the federal website is not yet working.

"It's a little like trying to sell someone something without actually showing them the price tag," he says. "Consumers are going to be skeptical until they have the information to be able to understand 'what is my true net cost.'"

Gary Lauer, CEO of online insurance giant eHealth, is also frustrated at his company's inability to sign up people who are eligible for subsidies. "We have an agreement with the federal government in the 36 states where they're operating an exchange to be able to do that, but frankly the technology's not working," he said.

Lauer says fully online companies like his are crucial for getting young people enrolled when the federal site can't accommodate them. And getting enough young healthy people to offset the older, sicker ones is critical to the success of the entire enterprise.

"Young people have grown up in front of monitors and keyboards; and now they communicate through their hands — through smartphone devices, through tablets," he says. "They don't want to go to a call center; they're not going to fill out paper applications like it's 1975. They want to do this online at 1 in the morning."

Shots is the online channel for health stories from the NPR Science Desk. We report on news that can make a difference for your health and show how policy shapes our health choices. Look to Shots for the latest on research and medical treatments, as well as the business side of health. Your hosts are Scott Hensley and Nancy Shute. You can reach the Shots team via our contact form.